In medical technology, peristaltic or occluding pumps may be used for reasons of sterility. Various designs of peristaltic pump are known, one of which is the roller pump. All peristaltic pumps have in common the fact that an elastic hose pipe is inserted into the pump, in which the liquid to be delivered flows.
The known extracorporeal blood treatment apparatuses are a particular area of application of peristaltic pumps in medical technology, said blood treatment apparatuses including for example hemodialysis apparatuses, hemofiltration apparatuses and hemodiafiltration apparatuses.
Great demands are made on the delivery accuracy of peristaltic pumps in medical technology, for example with extracorporeal blood treatment apparatuses. It is a drawback that the effective delivery rate of a peristaltic pump, which is typically adjusted at a preset nominal speed of the pump, depends on a large number of factors. From the nominal speed of the pump, therefore, it is not readily possible to draw conclusions about its effective delivery rate.
The properties of the hose pipe represent one of the main factors from which the delivery rate of a peristaltic pump depends. It has been shown in practice that a deformation of the elastic hose leads to a change in the delivery rate of the pump.
German patent document DE 197 47 254 C2 describes a method for the non-invasive internal pressure measurement in elastic hose pipes. The document points out that the properties of the hose pipe change with time.
There is known from U.S. Pat. No. 6,691,047 a method for calibrating a peristaltic pump for an extracorporeal blood treatment apparatus, whereby the pressure in the hose pipe is measured upstream of the pump before the start of the blood treatment, in order to be able to predict the pressure upstream of the pump in the course of the treatment. The pump is calibrated at a pressure which corresponds to the average value of the previously measured pressure.
U.S. Pat. No. 4,715,786 describes a method for calibrating a peristaltic pump, but without taking account of a dependence of the delivery rate on time.
PCT publication WO 99/23386 describes a method for controlling the speed of peristaltic pumps as a function of the pressure in the hose pipe upstream of the pump. The control takes place on the basis of the physical properties of the hose pipe and the pump, but once again without taking account of the dependence on time.
There is known from U.S. Pat. No. 5,733,257 a calibration method for peristaltic pumps, wherein the dependence of the delivery rate on time is negated, in that the calibration does not take place until after the lapse of a preset duration. It is assumed that the delivery rate after the lapse of this duration no longer changes with time.
The method described in European patent document EP 0 513 421 A1 for determining the blood flow during an extracorporeal blood treatment likewise does not take account of the time-related change in the delivery rate with the running time of the pump.